1. Field of the Invention
Example embodiments of the present invention relate to a method of manufacturing a semiconductor memory device. More particularly, example embodiments of the present invention relate to a method of manufacturing a semiconductor device including a single-crystalline thin film transformed from an amorphous thin film having an amorphous material.
2. Description of the Related Art
Materials are generally divided into single-crystalline materials, polycrystalline materials and amorphous materials. A single-crystalline material is one that has a single crystal unit structure, while a polycrystalline material has a structure including a plurality of crystal units. An amorphous material may not include a defined crystal structure, as atoms in the amorphous material may be irregularly bonded to each other. The polycrystalline material typically has many grain boundaries due to the plurality of crystal structure units. The movement of carriers, such as electrons or holes, may be restricted in the polycrystalline material by such grain boundaries. To reduce and/or to minimize such reductions in carrier mobility, a single-crystalline silicon thin film is often used as an active region of a semiconductor device including a thin-film transistor (TFT) having a stacked structure, an active region of a system-on-chip (SOC) device or an active region of a NAND flash memory device. The single-crystalline silicon thin film may include a high density of large single-crystalline grains.
The present inventors filed Korean Patent Application No. 2005-22509 on Mar. 18, 2005, which describes a method of forming a single-crystalline silicon thin film from an amorphous silicon thin film, and which was registered as Korean Patent No. 599,043 on Jul. 4, 2006.
In Korean Patent No. 599,043, an amorphous silicon thin film is formed on a seed layer including single-crystalline silicon, and then a laser beam is irradiated onto the amorphous silicon thin film so as to change the amorphous silicon thin film into the single-crystalline silicon thin film. A single-crystalline silicon thin film, which has a high density of relatively large single-crystalline grains, may be easily formed by the above-described method. FIG. 1 is a cross-sectional view illustrating a semiconductor device including a single-crystalline silicon thin film by a conventional method.
Referring to FIG. 1, Korean Patent No. 599,043 discloses the method of forming a single-crystalline silicon thin film 32 serving a channel layer employed only in a volatile memory device, such as a dynamic random access memory (DRAM) device, and not in a non-volatile memory device, such as a NAND flash memory device. Further, in Korean Patent No. 599,043, the amorphous silicon thin film may be transformed using silicon included in one seed layer 28 as a seed into the single-crystalline silicon thin film having a sufficiently enlarged width. However, when the amorphous silicon thin film is spaced apart from the seed layer 32 by a distance of over about 4 to about 5 μm, it may be difficult to form the single-crystalline silicon thin film 32 having uniform characteristics.
When the seed layer 28 is formed on a substrate 10 by a selective epitaxial growth process, defects D may occur in the seed layer 28 due to a thermal budget or a sidewall of an insulation layer pattern 16. The defects D may have an orientation in the crystallographic (111) direction. When the amorphous silicon thin film is transformed using the seed layer 28 as a seed to form the single-crystalline silicon thin film 32 that may serve as a channel layer, an upper portion of the single-crystalline silicon thin film 32 may include the defects D being oriented in the crystallographic (111) direction. Since the defects D having an orientation of about 54.7° from a crystallographic point of view of the cubic structure is transcribed from the seed layer 28 into the single-crystalline silicon thin film 32, the single-crystalline silicon thin film 32 having a relatively thin thickness may also include the defects D at the upper portion thereof.